**4. Liming**

Most soils cultivated with sugarcane in the world are acidic, presenting a low saturation by basic cations such as calcium, magnesium, and potassium. Deficiency of basic cations, associated with high levels of aluminum, iron, and manganese, is detrimental to the growth of the root system and, consequently, of the sugarcane plant as a whole. Al(OH)<sup>2</sup> + and Al3+ are phytotoxic forms of aluminum that affect cell division, inhibit root growth, cause phosphorus precipitation both in the soil and inside roots, decrease the absorption of water and nutrients, and affect photosynthesis and, consequently, crop productivity. After applying limestone, there is an increase in the soil pH, and a neutralization of soil acidity precipitates aluminum and makes phosphorus available. Studies conducted by [6] on Purple Latosol showed that a pH increase from 4.0 to 5.0 precipitates aluminum totally and raises the phosphorus content from 4.8 to 24.2 mg/dm3 (**Table 1**).

simple samples, in handling and transporting a small soil volume in field before homogenization of simple samples, and in collecting composite samples. On the other hand, a low volume of collected soil causes variability of soil fertility indexes to increase, making it necessary to collect a high number of simple samples to form a representative composite sample. Even so, the laboriousness of soil sampling using augers is less than when using straight blades. At first, the use of instruments that collect a small soil volume, such as augers, would not be recommended for areas of minimal or no-tillage, where fertilization is performed in planting lines, preferring in such cases straight blades [1]. Regardless of the material used for sampling, care should be

In large areas, grid soil sampling has been used. This technique consists in the collection of georeferenced soil samples. Due to georeferencing, it is possible to measure the variability of soil nutrient contents and to apply acid and fertilizer correctives at variable levels. In the traditional collection system, to obtain a composite sample, one must collect between 10 and 30 simple samples, numbers that depend on the size of the area and its homogeneity. On average, five simple samples per hectare are collected. After air-drying the composite sample, approximately 500 g of soil is collected to be packed in a properly identified container and

In Brazil, potassium, calcium, magnesium, sodium, and aluminum are analyzed as for exchangeable contents, and even though there is a great variation in the chemical extractors used by different laboratories, the accuracy of such analyses is high. Phosphorus, however, presents a greater reactivity with the soil, and its dynamics is also more complex. Thus, there are questions about the results of analyses performed in laboratories using different methods and extractors. However, analyses carried out by authors on soils from sugarcane regions in the state of Minas Gerais, Brazil, not fertilized with natural phosphate, indicated that there was no significant difference between available phosphorus levels extracted using Mehlich in relation to levels obtained using ion exchange resin. Sulfur and micronutrient contents varied greatly in relation to method and extractor used in soil chemical analysis, and there is still a great influence of collection time, soil moisture, and sample preparation [5]. Thus, the history of the area is of great value, especially regarding micronutrients, because if there is a record of deficiency in previous crops, it becomes necessary to include such deficient elements in fertilization.

Most soils cultivated with sugarcane in the world are acidic, presenting a low saturation by basic cations such as calcium, magnesium, and potassium. Deficiency of basic cations, associated with high levels of aluminum, iron, and manganese, is detrimental to the growth of

phytotoxic forms of aluminum that affect cell division, inhibit root growth, cause phosphorus precipitation both in the soil and inside roots, decrease the absorption of water and nutrients, and affect photosynthesis and, consequently, crop productivity. After applying limestone, there is an increase in the soil pH, and a neutralization of soil acidity precipitates aluminum and makes phosphorus available. Studies conducted by [6] on Purple Latosol showed that a

+

and Al3+ are

the root system and, consequently, of the sugarcane plant as a whole. Al(OH)<sup>2</sup>

taken to always remove the same soil volume from each single sample.

sent to a chemical analysis laboratory.

172 Sugarcane - Technology and Research

**4. Liming**

The use of nitrogen fertilizers, mainly ammoniacal, and the removal of basic cations by harvesting may also contribute to soil acidity, which is why it has been common practice in sugarcane crops to correct soil acidity. Acidification caused by an ammoniacal fertilizer, ammonium sulfate, (NH<sup>4</sup> )2 SO4 , is exemplified below:

$$\text{(NH}\_4\text{)}\_2\text{SO}\_4 \leftrightarrow 2\text{NH}\_4^+ + \text{SO}\_4^{2-} \tag{1}$$

then 2NH<sup>4</sup> + originating from the dissociation of (NH<sup>4</sup> ) 2 SO4 is oxidized by Nitrosomonas and Nitrobacter, producing 2NO3 − . Thus, the acid reaction of ammonium sulfate can be described as:

$$\text{(NH}\_4\text{)}\_2\text{SO}\_4 + 4\text{O}\_2 \rightarrow 2\text{NO}\_3^- + \text{SO}\_4^- + 2\text{H}\_2\text{O} + 4\text{H}^+\tag{2}$$

Since 100 g of CaCO3 neutralizes 2.0 moles of 2H<sup>+</sup> , to neutralize 4H<sup>+</sup> , 200 g of CaCO3 is required. Several materials can be used as soil acidity correctors. The most used are calcitic limestones, magnesium and dolomitic limestones, and calcium and magnesium silicates, called steel plant slags. In these slags, the magnesium oxide content oscillates around 8%, while calcitic limestones have MgO contents lower than 5%, magnesium levels between 6 and 12%, and dolomitic levels above 12%. The efficiency of these products in the correction of soil acidity depends, among other factors, on their particle size, a uniform distribution in the field, and soil water availability. In relation to the corrective dose, there are some methods to estimate the quantity of product to be applied. Such methods are based on the particle size and neutralizing power of the corrective, as well as soil chemical characteristics, mainly calcium, magnesium, potassium, aluminum, and hydrogen contents.

In the majority of Brazilian states, the corrective dose to be applied is estimated by neutralization of exchangeable acidity and increase in calcium and magnesium contents [7], or base saturation [8]. For sugarcane, it has been recommended to increase base saturation (V) to 60%. According to [8], the amount of limestone (QC) to be used, when adopting the base saturation criterion, is calculated by the following expression:

QC (t ha<sup>−</sup>1) = [(60–V) × T]/PRNT (3)


**Table 1.** Neutralization of soil acidity using CaCO3 , increase in pH, precipitation of aluminum, and availability of phosphorus from a Purple Latosol.

where V is the current base saturation of the soil, T is the cation exchange capacity at pH 7.0, and PRNT is the relative total neutralizing power of the corrective used.

Studies conducted by [9] on soils cultivated with sugarcane in the Minas Gerais state showed a need to use twice as many corrective levels as calculated using both methods [7, 8] to neutralize exchangeable aluminum or increase base saturation to 60% (**Figure 2**). Results similar to those described by [9] were obtained by [10–12] by comparing analytical methods to assess the need for limestone in the states of Santa Catarina, Paraná, and Mato Grosso. The authors also verified that base saturation underestimated at a high degree the need for limestone by the soils studied, especially the most buffered ones. Base saturation values lower than those predicted analytically were also found by [13] in a medium texture, alkaline Latosol cultivated with sugarcane. Ref. [12] in Campo Novo do Parecis and Nova Mutum (MT) verified that the increase in limestone doses estimated by base saturation ranged from 46 to 92%. Considering the observations of [10–13], the authors recommended that, for areas with base saturation values below 30% or more clayey soils, the amount of limestone to be applied is 1.5–2.0 times as that calculated by Eq. (3) [8].

In large sugarcane crops, many types of limestone distributors have been used, but, for small producers, the application is manual for most of the time. One method that authors have recommended for small producers is to demarcate a square or a rectangle with the limestone itself and, in this area, apply a corrective volume corresponding to the recommended dose. For example, supposing that the recommended dose was 4000 kg and the density of this correction is 1.25 kg/L, then 3200 L of corrective should be applied per hectare, or 0.32 L of the corrective/m2 . One of the options for the producer to manually distribute limestone would be to demarcate 50 m2 areas with the limestone itself and apply 12.8 L of limestone. In **Figure 3**, a small sugarcane producer is applying limestone using this method to demarcate an area. Two bamboo sticks, spaced 10 m apart, can be seen at the bottom, with a plastic tape tied at the edge to serve as a marking for the demarcation of lines.

There is a generalized conceptualization that the best Ca+2:Mg+2 ratio in the soil is 4:1. Therefore, the type of limestone (calcitic, magnesian, or dolomitic) to be used should be based on this ratio. On the other hand, some authors recommend exchangeable cation saturation in relation to the effective cation exchange capacity of the soil (t) at 80% of calcium, 13% of magnesium, and 6% of potassium, providing Ca:Mg, Ca:K, and Mg:K ratios of 6.15:1, 13.3:1, and 2.2:1, respectively. However, several studies have shown that the concentrations of Ca and Mg in the solution are more important than the relation between these cations [14]. In the case of corn, studies conducted by [14] indicated that variations in the soil Ca:Mg ratio from 1:1 to

**Figure 3.** Equipment for the distribution of limestone in large sugarcane plantations, and a small rural producer applying

The sugarcane plantation areas and sugarcane planting using minimum and no-tillage systems have increased, following the tendency of corn and soybeans. In these systems, limestone is not incorporated as in the conventional tillage. However, the mineralization of crop remains and sugarcane straw, similar to what occurs in no-tillage areas with annual crops, releases organic anions that complex with Ca, Mg, K, and Al, forming electrically neutral molecules that percolate in the soil. In addition, such organic anions neutralize part of the soil acidity. Therefore, in such areas, liming should be performed only when base saturation at the 0–20 cm layer is lower than 40%. In a study conducted by [3] using lysimeters, it was verified that the sum of cation charges (K, Ca, Mg, and Na) was always greater than the sum of anion charges (nitrate, sulfate, and chloride) for the whole experimental period. Sulfate was the mineral anion with the highest concentration in the solution percolated in the soil, followed by chloride and nitrate. Initially, organic anions represented only 40% of the total negative charge, but there was a gradual and constant increase of these anions in the ionic balance of the percolated solution and, at the end of the experimental period, their share of the solution's electroneutrality increased to 70%. Such results confirm, as in other studies, that organic anions originating from the mineralization of sugarcane remains or released by sugarcane roots must be involved in the nutrient leaching process by organometallic complexation with Ca, Mg, K, Al, and Na, which

dm−3, respec-

Mineral Nutrition and Fertilization of Sugarcane http://dx.doi.org/10.5772/intechopen.72300 175

12:1 in soils with exchangeable Ca and Mg contents above 2.32 and 0.40 cmolc

tively, did not affect yield and production of corn dry matter.

are present in the soil solution.

limestone to previously demarcated areas.

**Figure 2.** Aluminum saturation (m%) at 40, 80, and 145 days after the beginning of incubation (DAI) of soil samples with dolomitic limestone and calcium silicate using one or two doses of corrective analytically predicted by base saturation.

where V is the current base saturation of the soil, T is the cation exchange capacity at pH 7.0,

Studies conducted by [9] on soils cultivated with sugarcane in the Minas Gerais state showed a need to use twice as many corrective levels as calculated using both methods [7, 8] to neutralize exchangeable aluminum or increase base saturation to 60% (**Figure 2**). Results similar to those described by [9] were obtained by [10–12] by comparing analytical methods to assess the need for limestone in the states of Santa Catarina, Paraná, and Mato Grosso. The authors also verified that base saturation underestimated at a high degree the need for limestone by the soils studied, especially the most buffered ones. Base saturation values lower than those predicted analytically were also found by [13] in a medium texture, alkaline Latosol cultivated with sugarcane. Ref. [12] in Campo Novo do Parecis and Nova Mutum (MT) verified that the increase in limestone doses estimated by base saturation ranged from 46 to 92%. Considering the observations of [10–13], the authors recommended that, for areas with base saturation values below 30% or more clayey soils, the amount of limestone to be applied is 1.5–2.0 times as that calculated by Eq. (3) [8].

In large sugarcane crops, many types of limestone distributors have been used, but, for small producers, the application is manual for most of the time. One method that authors have recommended for small producers is to demarcate a square or a rectangle with the limestone itself and, in this area, apply a corrective volume corresponding to the recommended dose. For example, supposing that the recommended dose was 4000 kg and the density of this correction is 1.25 kg/L, then 3200 L of corrective should be applied per hectare, or 0.32 L of the

a small sugarcane producer is applying limestone using this method to demarcate an area. Two bamboo sticks, spaced 10 m apart, can be seen at the bottom, with a plastic tape tied at

**Figure 2.** Aluminum saturation (m%) at 40, 80, and 145 days after the beginning of incubation (DAI) of soil samples with dolomitic limestone and calcium silicate using one or two doses of corrective analytically predicted by base saturation.

the edge to serve as a marking for the demarcation of lines.

. One of the options for the producer to manually distribute limestone would be

areas with the limestone itself and apply 12.8 L of limestone. In **Figure 3**,

and PRNT is the relative total neutralizing power of the corrective used.

corrective/m2

to demarcate 50 m2

174 Sugarcane - Technology and Research

**Figure 3.** Equipment for the distribution of limestone in large sugarcane plantations, and a small rural producer applying limestone to previously demarcated areas.

There is a generalized conceptualization that the best Ca+2:Mg+2 ratio in the soil is 4:1. Therefore, the type of limestone (calcitic, magnesian, or dolomitic) to be used should be based on this ratio. On the other hand, some authors recommend exchangeable cation saturation in relation to the effective cation exchange capacity of the soil (t) at 80% of calcium, 13% of magnesium, and 6% of potassium, providing Ca:Mg, Ca:K, and Mg:K ratios of 6.15:1, 13.3:1, and 2.2:1, respectively. However, several studies have shown that the concentrations of Ca and Mg in the solution are more important than the relation between these cations [14]. In the case of corn, studies conducted by [14] indicated that variations in the soil Ca:Mg ratio from 1:1 to 12:1 in soils with exchangeable Ca and Mg contents above 2.32 and 0.40 cmolc dm−3, respectively, did not affect yield and production of corn dry matter.

The sugarcane plantation areas and sugarcane planting using minimum and no-tillage systems have increased, following the tendency of corn and soybeans. In these systems, limestone is not incorporated as in the conventional tillage. However, the mineralization of crop remains and sugarcane straw, similar to what occurs in no-tillage areas with annual crops, releases organic anions that complex with Ca, Mg, K, and Al, forming electrically neutral molecules that percolate in the soil. In addition, such organic anions neutralize part of the soil acidity. Therefore, in such areas, liming should be performed only when base saturation at the 0–20 cm layer is lower than 40%.

In a study conducted by [3] using lysimeters, it was verified that the sum of cation charges (K, Ca, Mg, and Na) was always greater than the sum of anion charges (nitrate, sulfate, and chloride) for the whole experimental period. Sulfate was the mineral anion with the highest concentration in the solution percolated in the soil, followed by chloride and nitrate. Initially, organic anions represented only 40% of the total negative charge, but there was a gradual and constant increase of these anions in the ionic balance of the percolated solution and, at the end of the experimental period, their share of the solution's electroneutrality increased to 70%. Such results confirm, as in other studies, that organic anions originating from the mineralization of sugarcane remains or released by sugarcane roots must be involved in the nutrient leaching process by organometallic complexation with Ca, Mg, K, Al, and Na, which are present in the soil solution.
